The Chicago White Sox have signed free agent​ left-handed reliever Zach Duke to a three-year, $15 million deal, the team announced Tuesday.

Duke, 31, was a starting pitcher for the Pittsburgh Pirates from 2005-10. Last season he was used in a new role as a reliever with the Milwaukee Brewers and posted a 5-1 record with a 2.45 ERA over 58 2/3 innings in 74 appearances.

White Sox general manager Rick Hahn said last week at the GM meetings that the team was exploring options to improve their bullpen, which posted a 4.38 ERA and ranked 28th out of 30 in the league.

"Very early on, we identified Zach as one of the best left-handed free agents available this offseason, so we are very pleased he agreed to join the White Sox," said Hahn in a statement announcing the deal. "He addresses an important need in our bullpen by giving [manager] Robin Ventura a veteran left-handed option late in games."